Engineering RNA interference-based resistance to dengue virus type 2 in genetically modified Aedes aegypti

Mosquitoes (Aedes aegypti) were genetically modified to exhibit impaired vector competence for dengue type 2 viruses (DENV-2). We exploited the natural antiviral RNA interference (RNAi) pathway in the mosquito midgut by constructing an effector gene that expresses an inverted-repeat (IR) RNA derived from the premembrane protein coding region of the DENV-2 RNA genome. The A. aegypti carboxypeptidase A promoter was used to express the IR RNA in midgut epithelial cells after ingestion of a bloodmeal. The promoter and effector gene were inserted into the genome of a white-eye Puerto Rico Rexville D (Higgs' white eye) strain by using the nonautonomous mariner MosI transformation system. A transgenic family, Carb77, expressed IR RNA in the midgut after a bloodmeal. Carb77 mosquitoes ingesting an artificial bloodmeal containing DENV-2 exhibited marked reduction of viral envelope antigen in midguts and salivary glands after infection. DENV-2 titration of individual mosquitoes showed that most Carb77 mosquitoes poorly supported virus replication. Transmission in vitro of virus from the Carb77 line was significantly diminished when compared to control mosquitoes. The presence of DENV-2-derived siRNAs in RNA extracts from midguts of Carb77 and the loss of the resistance phenotype when the RNAi pathway was interrupted proved that DENV-2 resistance was caused by a RNAi response. Engineering of transgenic A. aegypti that show a high level of resistance against DENV-2 provides a powerful tool for developing population replacement strategies to control transmission of dengue viruses.

Gonotrophic cycle and survivorship of Culex quinquefasciatus (Diptera: Culicidae) using sticky ovitraps in Monterrey, northeastern Mexico

Mark-release-recapture experiments were conducted to determine the length of the gonotrophic cycle and rate of survivorship of Culex quinquefasciatus Say in Monterrey, northeastern Mexico. A total of 2,352 field-caught Cx. quinquefasciatus females were marked and released at 8-12 h postemergence in 2 field trials. Sticky ovitraps were used to recapture marked gravid females. One hundred and ten (4.6%) marked females were recaptured during a 12-day sampling period. Recapture rates for the 2 individual trials were 6.4% and 3.5%. The length of the gonotrophic cycle, calculated as the average time between the initial blood meal and the time of recapture of gravid females, was 2-3 days. The first blood-fed mosquitoes were recaptured on the 2nd day postrelease. Gravid egg-laying females were most commonly recaptured at 2-3 days postfeeding. Daily survival estimates for the 2 release dates were of 0.871 and 0.883, respectively.

Control of arbovirus diseases: is the vector the weak link?

Arthropod-borne virus (arbovirus) diseases (ABVDs) remain major threats to human health and well-being and, as an epidemiologic group, inflict an unacceptable health and economic burden on humans and animals, including livestock. The developed world has been fortunate to have escaped much of the burden that arboviruses and their arthropod vectors inflict on humans in disease endemic countries, but the introduction and rapid spread of West Nile virus in the Western Hemisphere demonstrated that we can no longer be complacent in the face of these emerging and resurging vector-borne diseases. Unfortunately, as the burdens and threats of ABVDs have increased, the U.S. and international public health capacity to address them has decreased. Vaccines are not available for most of these agents. Previously successful strategies to control ABVDs emphasized vector control, but source reduction and vector control strategies using pesticides have not been sustainable. New insights into vector biology and vector pathogen interactions, and the novel targets that likely will be forthcoming in the vector post-genomics era, provide new targets and opportunities for vector control and disease reduction programs. These findings and approaches must be incorporated into existing strategies if we are to control these important pathogens.

Quantitative analysis of La Crosse virus transcription and replication in cell cultures and mosquitoes

La Crosse (LAC) virus (family Bunyaviridae, genus Orthobunyavirus) small (S) segment negative-sense RNA genome (vRNA), positive-sense full-length RNA complement (vcRNA), and subgenomic mRNA were assayed in infected cell cultures and female Aedes (Ochlerotatus) triseriatus mosquito tissues using quantitative PCR (Q-PCR). During persistent infection of C6/36 (Aedes albopictus) and MAT (Aedes triseriatus) cultured cells and cytolytic infection of BHK-21 cultured cells, LAC vRNA was the most abundant RNA species, followed by mRNA and vcRNA. RNA copy numbers per cell were quantified and vRNA correlated to virus titer in cell culture medium. The Q-PCR assay proved more sensitive than reverse transcription (RT)-PCR and immunofluorescence assays (IFA) for detecting LAC virus infection of mosquitoes. After infection of female mosquitoes orally, quantities of LAC RNA increased in ovaries for 6 days, and as ovarian biosynthetic activity quiesced, LAC RNA quantities decreased then remained detectable at a low level. After a second, noninfectious blood meal, quantities of LAC RNA in ovaries increased significantly, quantitatively confirming correlation of LAC virus RNA synthesis with vector metabolic activity. Coregulation of viral replication and mosquito ovary metabolic activity may condition efficient transovarial transmission.

Comparison of commercially available and novel West Nile virus immunoassays for detection of seroconversion in pig-tailed macaques (Macaca nemestrina)

We report the assessment and validation of an NS1 epitope-blocking enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to West Nile virus (WNV) in macaques. Sera from naturally infected Macaca nemestrina were tested by ELISA and plaque reduction neutralization test (PRNT). Results were correlated with hemagglutination inhibition (HAI) data. Our results demonstrate that the blocking ELISA rapidly and specifically detects WNV infection in M. nemestrina. In addition, the diagnostic value of 7 commercially available immunoassays (PanBio immunoglobulin [Ig] M ELISA, PanBio IgG ELISA, PanBio immunofluorescence assay (IFA), InBios IgG ELISA, InBios IgM ELISA, Focus Diagnostics IgG ELISA, and Focus Diagnostics IgM ELISA) in M. nemestrina was evaluated and compared with that of the epitope-blocking ELISA. The PanBio IgG ELISA was found to effectively diagnose WNV exposure in M. nemestrina. Further, PanBio IFA slides are fast and reliable screening tools for diagnosing flaviviral exposure in M. nemestrina.

Molecular epidemiology of Bluetongue virus in northern Colorado

The molecular epidemiology of Bluetongue virus serotype 11 (BTV11) in an enzootic focus in northern Colorado was investigated. Viruses isolated up to 12 years apart, from both vertebrate and invertebrate hosts, were compared by phylogenetic analysis of nucleotide sequence data from three genome segments: L2, S7, and S10. For each segment, viruses isolated from ruminants in the 1980s were more similar to one another than to viruses isolated from Culicoides spp. insects in the 1990s. Nearly identical BTV11-L2 segments were found in all isolates, but over time they were associated with different S7 and S10 genome segments. Therefore, L2-segment-based serologic identification of BTV isolates underestimates the origin and natural evolution of the viruses. In addition, the use of one or even two genome segments is inadequate to define the molecular epidemiology of the viruses in an enzootic focus. This information could influence import/export regulations based on BTV epidemiology in enzootic areas, as well as our view of the natural biology of the viruses.

Sindbis virus induces transport processes and alters expression of innate immunity pathway genes in the midgut of the disease vector, Aedes aegypti

The midgut of hematophagous insects is the initial site of infection by arthropod-borne viruses (arboviruses) and plays a crucial role in vector competence. To further understand processes that occur in the midgut in response to infection by an arbovirus, DNA microarrays were used to analyze gene expression changes following infection by the alphavirus, Sindbis (MRE16 Malaysian strain). Midgut transcription profiles from mosquitoes fed blood containing 10(8)pfu/ml of virus were compared with those from mosquitoes ingesting blood meals having no virus. Transcription profiles from both experimental groups were analyzed at 1, 4, and 8 days post-feeding. Among the many transcription changes observed by microarray analysis, the most dramatic involved three genes that had 25-40-fold increases in transcript levels in virus infected mosquitoes at 4 days post-infection. These genes were synaptic vesicle protein-2 (SV2), potassium-dependent sodium/calcium exchanger (NCKX), and a homologue of Caenorhabditis elegans Unc-93, a putative component of a two-pore potassium channel. We speculate that these changes represent changes in vesicle transport processes. In addition to these observations, transcript changes were observed in infected mosquitoes that suggested involvement of Toll and c-jun amino terminal kinase immune cascades as a response to viral infection.

Persistence of antibodies to West Nile virus in naturally infected rock pigeons (Columba livia)

Wild caught rock pigeons (Columba livia) with antibodies to West Nile virus were monitored for 15 months to determine antibody persistence and compare results of three serologic techniques. Antibodies persisted for the entire study as detected by epitope-blocking enzyme-linked immunosorbent assay and plaque reduction neutralization test. Maternal antibodies in squabs derived from seropositive birds persisted for an average of 27 days.

Experimental Transmission of West Nile Virus (Flaviviridae: Flavivirus) byCarios capensisTicks from North America

Seabird soft ticks, Carios capensis (Ixodida: Argasidae), originally collected from coastal Georgia, USA, were allowed to ingest a blood meal from pekin ducklings (Anas domesticus) infected with WNV. After 35 days of extrinsic incubation, the ticks transmitted virus to naive ducklings. WNV was detected via plaque assay and RTPCR in ticks and in tissues and serum of ducklings 7 days post infestation.

An analysis of gene flow among midwestern populations of the mosquito Ochlerotatus triseriatus

A population genetics study of the mosquito Ochlerotatus triseriatus was performed on 36 collections from adjoining regions of Iowa, Minnesota, and Wisconsin covering approximately 120 km(2). Single nucleotide polymorphism analysis was used to estimate variation in the mitochondrial NADH dehydrogenase subunit 4 (ND4) gene. The heated oligonucleotide ligation assay was used to identify the ND4 haplotype of each mosquito. No evidence of genetic isolation by distance was found, nor did Interstate 90 or the Mississippi River serve as barriers to gene flow. The effective migration rate varied from 18 to 45 reproductive migrants/generation, which is similar to estimates from an earlier study. The collections belong to a single, large, panmictic population. However, within this panmictic population, local genetic drift arises, possibly due to one or a few females ovipositing in larval breeding containers. From generation to generation, there is sufficient gene flow to mix families arising from individual breeding sites and eliminate founder effects due to drift.

Population dynamics of a diverse rodent assemblage in mixed grass-shrub habitat, southeastern Colorado, 1995-2000

We followed seasonal and year-to-year population dynamics for a diverse rodent assemblage in a short-grass prairie ecosystem in southeastern Colorado (USA) for 6 yr. We captured 2,798 individual rodents (range, one to 812 individuals per species) belonging to 19 species. The two most common species, deer mice (Peromyscus maniculatus) and western harvest mice (Reithrodontomys megalotis), generally had population peaks in winter and nadirs in summer; several other murid species demonstrated autumn peaks and spring nadirs; heteromyids were infrequently captured in winter, and populations generally peaked in summer or autumn. Inter-annual trends indicated an interactive effect between temperature and precipitation. Conditions associated with low rodent populations or population declines were high precipitation during cold periods (autumn and winter) and low precipitation during warm periods (spring and summer). Severity of adverse effects varied by species. Heteromyids, for example, were apparently not negatively affected by the hot, dry spring and summer of 2000. Cross-correlations for the temporal series of relative population abundances between species pairs (which are affected by both seasonal and interannual population dynamics) revealed positive associations among most murids and among most heteromyids, but there were negative associations between murids and heteromyids. These results have important implications for those attempting to model population dynamics of rodent populations for purposes of predicting disease risk.

Epizootiology of Sin Nombre and El Moro Canyon hantaviruses, southeastern Colorado, 1995-2000

Sin Nombre virus (SNV) is an etiologic agent of hantavirus pulmonary syndrome. To better understand the natural history of this virus we studied population dynamics and temporal pattern of infection of its rodent hosts in southeastern Colorado (USA) from 1995 to 2000. We present evidence for the presence of two hantaviruses, SNV in deer mice (Peromyscus maniculatus) and El Moro Canyon virus in western harvest mice (Reithrodontomys megalotis), at our study sites. Sin Nombre virus appeared only sporadically in deer mouse populations; overall prevalence of antibody to SNV was 2.6%. El Moro Canyon virus was enzootic: seroconversions occurred throughout the year; antibody prevalence (11.9% overall) showed a delayed-density-dependent pattern, peaking as relative abundance of mice was declining. Males of both host species were more frequently infected than were females. An apparently lower mean survivorship (persistence at the trapping site) for SNV antibody-positive deer mice could indicate a detrimental effect of SNV on its host, but might also be explained by the fact that antibody-positive mice were older when first captured.

Association mapping of segregating sites in the early trypsin gene and susceptibility to dengue-2 virus in the mosquito Aedes aegypti

Evidence suggests that midgut trypsins in Aedes aegypti condition the mosquito's ability to become infected with the dengue-2 flavivirus (DEN2). The activity of early trypsin protein peaks approximately 3 h after blood feeding and then drops within a few hours. We use association mapping to test the hypothesis that segregating sites in early trypsin condition midgut susceptibility to DEN2 virus. A total of 1642 females from throughout Mexico and the southern US were fed an artificial blood meal containing DEN2. After 2 weeks, mosquito heads and midguts were tested for DEN2. Mosquitoes with an infected head were classified as susceptible, those without a midgut infection had an infection barrier, and those with an infected gut but no head infection had an escape barrier. The early trypsin gene was amplified in two overlapping pieces from each mosquito and analyzed for single strand conformation polymorphisms (SSCPs). Unique SSCP genotypes were sequenced and 90 segregating sites were found. The dataset was divided into the four geographic regions within which Ae. aegypti is panmictic in Mexico. Heterogeneity chi2 analyses between alleles or genotypes and infection phenotypes demonstrated significant associations but allelic and genotypic effects were inconsistent among geographic regions. No consistent associations were found between segregating sites in early trypsin and susceptibility to DEN2 in Ae. aegypti in Mexico.

Serologic evidence of exposure of wild mammals to flaviviruses in the central and eastern United States

Serosurveys were conducted to obtain flavivirus and West Nile virus (WNV) seroprevalence data from mammals. Sera from 513 small- and medium-sized mammals collected during late summer and fall 2003 from Colorado, Louisiana, New York, Ohio, and Pennsylvania were screened for flavivirus-specific antibodies. Sera samples containing antibody to flaviviruses were screened for WNV-specific antibodies by epitope-blocking enzyme-linked immunosorbent assays and confirmed with plaque reduction neutralization tests. Prevalence of WNV antibodies among study sites ranged from 0% to 42.8% among the mammal communities sampled. High prevalence rates for WNV were noted among raccoons (100%, with a very small sample size, N = 2), Virginia opossums (50.0%), fox squirrels (49.1%), and eastern gray squirrels (48.3%). The high WNV antibody prevalence noted for tree squirrels, the peri-domestic tendencies of several of these species, and their ease of observation could make these species useful sentinels for monitoring WNV activity within urban communities.

Climatic factors and the occurrence of vesicular stomatitis in New Mexico, United States of America

Vesicular stomatitis (VS) outbreaks occurred in the southwestern United States of America in 1995, 1997 and 1998. The epidemiology of VS is not understood completely and some of the epidemiologic aspects of this disease are currently under investigation. In this study, daily maximum temperature, daily minimum temperature, daily mean temperature, daily mean relative humidity and daily total precipitation were collected at the Sevilleta Long Term Ecological Research site in central New Mexico. Discriminant analysis was used to identify the climatic variables best able to classify in which months VS would occur. The study found that the amounts of precipitation occurring two, ten, eleven and twelve months prior to the month in which cases were diagnosed, were the climatic variables that best described the occurrence of VS cases. The association of VS cases and precipitation suggests that, like numerous other arthropod-borne diseases, transmission of the disease-causing pathogen is linked to variations in climate.

Quantitative trait loci that control dengue-2 virus dissemination in the mosquito Aedes aegypti

The mosquito Aedes aegypti is the most important vector of yellow fever and dengue fever flaviviruses. Ae. aegypti eradication campaigns have not been sustainable and there are no effective vaccines for dengue viruses. Alternative control strategies may depend upon identification of mosquito genes that condition flavivirus susceptibility and may ultimately provide clues for interrupting transmission. Quantitative trait loci affecting the ability of Ae. aegypti to develop a dengue-2 infection in the midgut have been mapped previously. Herein we report on QTL that determine whether mosquitoes with a dengue-2-infected gut can then disseminate the virus to other tissues. A strain selected for high rates of dengue-2 dissemination was crossed to a strain selected for low dissemination rates. QTL were mapped in the F(2) and again in an F(5) advanced intercross line. QTL were detected at 31 cM on chromosome I, at 32 cM on chromosome II, and between 44 and 52 cM on chromosome III. Alleles at these QTL were additive or dominant in determining rates of dengue-2 dissemination and accounted for approximately 45% of the phenotypic variance. The locations of dengue-2 midgut infection and dissemination QTL correspond to those found in earlier studies.

Studies on overwintering of bluetongue viruses in insects

Bluetongue viruses (BTVs) are economically important arboviruses that affect sheep and cattle. The overwintering mechanism of BTVs in temperate climates has eluded researchers for many years. Many arboviruses overwinter in their invertebrate vectors. To test the hypothesis that BTVs overwinter in their vertically infected insect vectors, Culicoides sonorensis larvae were collected from long-term study sites in northern Colorado, USA, and assayed for the presence of BTV RNA by nested RT-PCR. Sequences from BTV RNA segment 7 were detected in 30 % (17/56) of pools composed of larvae and pupae collected in 1998 and in 10 % (31/319) of pools composed of adults reared from larvae collected in 1996. BTV was not isolated from the insects. Additionally, Culicoides cell-culture lines derived from material collected at one of the sites, or derived from insect samples collected during a BTV outbreak, contained BTV RNA segment 7. In contrast, segment 2 RNA was detected at half the rate of segment 7 RNA in the field-collected larvae and was only detected in the Culicoides cell lines with one of two primer sets. These data suggest that BTVs could overwinter in the insect vector and that there is reduced expression of the outer capsid genes during persistent infection.

Selection of D2S3, an Aedes aegypti (Diptera: Culicidae) strain with high oral susceptibility to Dengue 2 virus and D2MEB, a strain with a midgut barrier to Dengue 2 escape

Family-based phenotypic selection was used to breed two genetic strains of Aedes aegypti L. that differ in susceptibility to infection with dengue serotype 2 virus (DEN-2) strain JAM1409. A Dengue 2 Susceptible on 3 chromosomes (D2S3) strain was bred from Ae. aegypti aegypti and Ae. aegyptiformosus P1 parents to have a high midgut infection rate (MIR) and a high disseminated infection rate (DIR). A Dengue 2 Midgut Escape Barrier (D2MEB) strain was bred from D2S3 and Houston P1 parents to have a high MIR and a low DIR. After selection in the F2 generation, single strand conformation polymorphism genotypes were determined at cDNA marker loci throughout the genome to test for Mendelian ratios and thereby identify regions containing deleterious or lethal alleles. Both strains were orally challenged with two other DEN-2 genotypes, two DEN-1 genotypes, one DEN-3 genotype, and two DEN-4 genotypes. There were significant differences in MIR and DIR for the different virus strains in both the D2S3 and the D2MEB mosquito lines.

RNA interference acts as a natural antiviral response to O'nyong-nyong virus (Alphavirus; Togaviridae) infection of Anopheles gambiae

RNA interference (RNAi) is triggered in eukaryotic organisms by double-stranded RNA (dsRNA), and it destroys any mRNA that has sequence identity with the dsRNA trigger. The RNAi pathway in Anopheles gambiae can be silenced by transfecting cells with dsRNA derived from exon sequence of the A. gambiae Argonaute2 (AgAgo2) gene. We hypothesized that RNAi may also act as an antagonist to alphavirus replication in A. gambiae because RNA viruses form dsRNA during replication. Silencing AgAgo2 expression would make A. gambiae mosquitoes more permissive to virus infection. To determine whether RNAi conditions the vector competence of A. gambiae for O'nyong-nyong virus (ONNV), we engineered a genetically modified ONNV that expresses enhanced GFP (eGFP) as a marker. After intrathoracic injection, ONNV-eGFP slowly spread to other A. gambiae tissues over a 9-day incubation period. Mosquitoes were then coinjected with virus and either control beta-galactosidase dsRNA (dsbetagal; note that "ds" is used as a prefix to indicate the dsRNA derived from a given gene throughout) or ONNV dsnsP3. Treatment with dsnsP3 inhibited virus spread significantly, as determined by eGFP expression patterns. ONNV-eGFP titers from mosquitoes coinjected with dsnsP3 were significantly lower at 3 and 6 days after injection than in mosquitoes coinjected with dsbetagal. Mosquitoes were then coinjected with ONNV-eGFP and dsAgAgo2. Mosquitoes coinjected with virus and AgAgo2 dsRNA displayed widespread eGFP expression and virus titers 16-fold higher than dsbetagal controls after 3 or 6 days after injection. These observations provide direct evidence that RNAi is an antagonist of ONNV replication in A. gambiae, and they suggest that the innate immune response conditions vector competence.

RNA interference, arthropod-borne viruses, and mosquitoes

RNA interference (RNAi) probably functions as an antiviral mechanism in most eukaryotic organisms. Variations in the activity of this antiviral pathway in mosquitoes could explain, in part, why some mosquitoes are competent vectors of medically important, arthropod-borne viruses (arboviruses) and others are not. There are three lines of evidence that show the RNAi pathway exists in Aedes species that transmit arboviruses. The first is that recombinant Sindbis viruses expressing a RNA fragment from a genetically unrelated dengue-2 virus (DENV-2) interfere with DENV-2 replication in Aedes aegypti mosquitoes by a mechanism similar to virus-induced gene silencing described in plants. The second is that transfection of C6/36 (Aedes albopictus) cells with either double-stranded RNA or synthetic small interfering RNAs derived from an arbovirus genome interferes with replication of the homologous virus. The third is that a hairpin DENV-2-specific RNA transcribed from a plasmid can generate virus-resistant C6/36 cells. We hypothesize that genetically modified mosquitoes can be generated that transcribe a flavivirus-specific dsRNA, triggering the RNAi response soon after ingestion of a blood meal. This could induce the RNAi pathway in the midgut prior to establishment of virus infection and profoundly change vector competence. Towards this goal, we are developing transgenic A. aegypti lines that are refractory to DENV by exploiting the RNAi pathway.

Phylogenetic analysis of West Nile virus, Nuevo Leon State, Mexico

West Nile virus RNA was detected in brain tissue from a horse that died in June 2003 in Nuevo Leon State, Mexico. Nucleotide sequencing and phylogenetic analysis of the premembrane and envelope genes showed that the virus was most closely related to West Nile virus isolates collected in Texas in 2002.

Introduction of the American/Asian genotype of dengue 2 virus into the Yucatan State of Mexico

A dengue (DEN) outbreak occurred in the Yucatan State of Mexico in 2002. Three isolates were obtained from patients presenting with DEN-like symptoms, and examined by partial nucleotide sequencing and phylogenetic analysis. The isolates were identified as DEN-2 viruses of the American-Asian genotype; this is the first report of this genotype in the Yucatan State. The DEN-2 viruses of the American-Asian genotype have been associated with more severe disease outcomes. Thus, its introduction into the Yucatan State presents a serious problem to public health authorities. During this outbreak, DEN virus infection was confirmed in 18% (282 of 1,560) of the patients who presented with DEN-like symptoms. Of these, 87 (31%) patients met the World Health Organization criteria for dengue hemorrhagic fever, including two patients who died. The majority (77%) of the patients experienced secondary infections in this epidemic.

Using RNA interference to develop dengue virus resistance in genetically modified Aedes aegypti

Diseases caused by arthropod-borne viruses are significant public health problems, and novel methods are needed to control pathogen transmission. We hypothesize that genetic manipulation of Aedes aegypti mosquitoes can profoundly and permanently reduce vector competence and subsequent transmission of dengue viruses (DENV) to human hosts. We have identified RNA interference (RNAi) as a potential anti-viral, intracellular pathway in the vector that can be triggered by expression of virus-specific, double stranded RNAs (dsRNAs) to reduce vector competence to DENV. We identified DENV-derived RNA segments using recombinant Sindbis viruses to trigger RNAi, that when expressed in mosquitoes ablate homologous DENV replication and transmission. We also demonstrated that heritable expression of DENV-derived dsRNA in cultured mosquito cells can silence virus replication. We now have developed a number of transgenic mosquito lines that transcribe the effector dsRNA from constitutive promoters such as immediate early 1 (baculovirus) and polyubiquitin (Drosophila melanogaster). We have detected DENV-specific small interfering RNAs, the hallmark of RNAi, in at least one of these lines. Surprisingly, none of these lines expressed dsRNA in relevant tissues (e.g., midguts) that will ultimately affect transmission. A major challenge now is to express the effector dsRNA from tissue-specific promoters to allow RNAi to silence virus replication at critical sites in the vector such as midguts and salivary glands. If successful, this strategy has the advantage of harnessing a naturally occurring vector response to block DENV infection in a mosquito vector and profoundly affect virus transmission.